This circuit is for traditional old-style telephone lines found in an American 1980s documentation. Components are common and the optical coupler can be replaced with an equivalent.
This circuit generates a pulsed tone whose frequency depends on C2 and whose flashing depends on...
This circuit of a Popular Electronics from the 80's selects tones around 60 Hz, acting as a filter...
This circuit samples the current in a load and in case of excessive value it activates a...